Among the aircraft landing assistance systems, the best known are the ILS systems, ILS standing for “Instrument Landing System”. ILS systems are instrument approach systems for aircraft equipped therewith. An ILS system supplies information assisting the pilot in his landing manoeuvre. Such systems therefore require specific instrumentation on board the aircraft as well as detection and guidance systems on the ground.
Another guidance system employed at airports is the MLS, MLS standing for “Microwave Landing System”. It provides precision guidance for a landing, regardless of the meteorological conditions.
The ILS and MLS systems are very expensive and bulky items of equipment both on the ground and on board the aircraft. Light aircraft cannot include the equipment needed to implement these systems as much for cost reasons as for lack of space.
Apart from these conventional means that are primarily used by commercial civil aviation, other solutions can be envisaged.
A first solution uses a satellite positioning system, this type of system being commonly designated by the acronym GNSS, standing for “Global Navigation Satellite System”. Among these positioning systems, the GPS system, GPS standing for “Global Positioning System”, is now the most widely used. The main drawback of the GNSS systems is their lack of robustness. In practice, this type of service is not always available and is sensitive to electromagnetic interference.
A second solution is to use a LIDAR system, LIDAR standing for “Light Detection And Ranging”. This locating system, which operates on the same principle as radars, uses lasers in the visible range, and even in the infrared range. This therefore makes it ineffective in unfavourable weather conditions.
Another solution consists in using a highly directional millimetre-wave radar. Millimetre-wave radars require a search phase to designate the target. They must also be positioned accurately relative to the runway. This solution is, furthermore, very costly and often requires an onboard responder on the aircraft. The responder is itself costly, bulky and heavy, and it consumes a lot of energy. It also has to be made redundant for operational safety reasons.
Other locating methods for automatically guiding unmanned aircraft have been proposed in the past. Notable among these is the international patent application referenced by the number WO2006/053868, which notably proposes using a radar on the ground and a multifunction beacon on board the aircraft. However, this method does not solve the problem of assisting in the landing of manned aircraft, notably when the environmental conditions are unfavourable, for example when visibility is almost zero in foggy weather.
One technique described in the international patent application WO 02/091595 makes it possible to guide an aircraft in the landing phase using an interrogator-responder exchange between the ground and the aircraft. However, this synchronous system requires significant specific equipment, both on the ground and on the aircraft. Furthermore, this system suffers from a significant blind spot close to the secondary radar on the ground and implementing such a system is complex because of the accuracy required.